As of January 2017, about 40 F-35's have been delivered during the year. Lot 10 was recently confirmed by the DoD which brings a total of 356 F-35's under contract. However, 240 F-35's have been delivered to those parties both in the US and nations abroad. The total, indicates Lockheed has completed its commitment for the F-35 most of the way through the Lot 9 contract for 57. The next 26 or so F-35's to be delivered will complete the contract for Lot 9 and Lockheed can begin delivering on Lot 10 soon after.
The Lockheed production line at any given time has about 45 F-35's in the assembly line located in Fort Worth Texas. Having made this observation, it would be safe to say Lockheed is already into Lot 10 work estimating about twenty out of the ninety contracted are lot ten as WIP (works in progress) planes on the factory floor. These are only estimates, but does give a relative view of delivered vs contract progress by year and Lot number.
A final note is that congress and the military agree on monies spent for Lot Work before a contract is signed and completed, so as to not interrupt the production flow. Suppliers get paid as does Lockheed using interim dollars for a continuos flow of F-35's. Lot 10 production started before its spending contract was passed and signed. The method uses advanced funding for maintaining a continuos production flow. Monies spent in advance will be adjusted affecting the "Lot's" contract balance after its signing.